This proposal is for the examination of those factors which determine cell number in the adipose tissue of man and animals. Specifically, the time course of development of obesity in subcutaneous, epididymal and retroperitoneal fat of the Zucker obese rat and Bar Harbor obese hyperglycemic mouse will be studied to compare these strains which have hyperplastic adipose tissue, with other genetic strains showing only cell hypertrophy. The effect of sex hormones on control of adipocyte number will also be evaluated since only the female Bar Harbor hyperglycemic mouse shows marked hyperplasia. The sequence of events in stromal tissue of the adipocyte organ that lead to mature adipocyte formation will be examined by the use of thymidine - methyl - H3 incorporation into DNA and a search for "marker" enzymes in pre-adipocytes. The nutritional, hormonal and genetic influence on the development of adipocytes from stromal precursor cells will then be studied.